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Date: Tue, 27 Sep 2016 05:14:14 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Chinner <david@fromorbit.com>,
        CAI Qian <caiqian@redhat.com>,
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        Jens Axboe <axboe@kernel.dk>, Nick Piggin <npiggin@gmail.com>,
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Subject: Re: [PATCH 04/12] splice: lift pipe_lock out of splice_to_pipe()
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On Mon, Sep 26, 2016 at 03:35:12PM +0200, Miklos Szeredi wrote:
> > -       if (spd.nr_pages <= 0)
> > -               ret = spd.nr_pages;
> > -       else
> > -               ret = splice_to_pipe(pipe, &spd);
> > -
> > +       pipe_lock(pipe);
> > +       ret = wait_for_space(pipe, flags);
> > +       if (!ret) {
> > +               spd.nr_pages = get_iovec_page_array(&from, spd.pages,
> > +                                                   spd.partial,
> > +                                                   spd.nr_pages_max);
> > +               if (spd.nr_pages <= 0)
> > +                       ret = spd.nr_pages;
> > +               else
> > +                       ret = splice_to_pipe(pipe, &spd);
> > +               pipe_unlock(pipe);
		    ^^^^^^^^^^^^^^^^
> > +               if (ret > 0)
> > +                       wakeup_pipe_readers(pipe);
> > +       }
> 
> Unbalanced pipe_lock()?

Reordering braindamage; fixed.

> Also, while it doesn't hurt, the constification of the "from" argument
> of get_iovec_page_array() looks only noise in this patch.

Rudiment of earlier variant, when we did a non-trivial loop in the caller.
Not needed anymore, removed.

Fixed variant force-pushed to the same branch